In cataract surgery, the crystalline lens or lens nucleus from the eye is removed and, most commonly, an artificial lens is implanted within the eye. When implanted, the lens is supported in either the anterior or posterior chamber of the eye by support means, such as one or more struts, that extend outwardly from the artificial lens.
U.S. Pat. No. 4,441,217 discloses various arrangements for intraocular lenses having a light focusing lens body with oppositely disposed support members. When implanted in the human eye, the support members contact natural regions of the eye and position the optical axis of the lens body at a point that is offset from the geometric center axis of the cornea. With such positioning, the optical axis of the lens is aligned with the pupillary axis of the eye. For other intraocular lens configurations see, for example, U.S. Pat. Nos. 4,513,456; 4,536,897; and 4,664,666.
The article entitled "Dual Vision Lenses Give a Better View" by J. Hecht in New Scientist, Mar. 10, 1990, at page 39, discloses a coated implant lens designed by the 3M Company that focuses on both near and distant objects. The lens uses a technology called "binary" or "diffractive" optics whereby light waves are scattered around the edges of objects in their path. The direction of scattering depends on both the shape of the object and the wavelength of light. The 3M lens is described as having one-half of a back surface covered with a series of stepped ridges (grating) which are no more than two micrometers high. This series of ridges combines with the refractive power of the lens to focus light from nearby objects onto the retina. Other areas of the lens not having a series of ridges focus light from distant objects onto the retina. It is explained that the brain ignores the out-of-focus light reaching the retina. In other words, the brain is capable of automatically shifting and discriminating between the two images. Therefore, the ridged lenses permit a patient to focus on both near and distant objects as if they were wearing bifocals. This avoids the need for patients to wear glasses to see nearby objects as normally required with the previously used plastic lenses.
The grating design of the 3M dual-focus lens is similar to a diffraction grating to control light spreading and to cause light to converge at a common focal point. Such diffraction grating at the various portions of the 3M lens degrades the lens, which degradation can be reduced by supplying finer and finer gratings. With diffraction optics only a small area of the 3M lens does the focusing. More particularly, light incident on the front surface of the 3M lens passes therethrough in normal fashion, and diffraction only takes place at the sharp edge of a ridge. Therefore, it is preferable to provide as many sharp ridges in the space of the 3M lens as possible to provide the diffractive focusing. However, a normal lens implant has a maximum diameter of about 5 mm, with most lenses being less than that, and only a limited quantity of ridges can be supplied in the 3M lens. In light of the above discussion, it appears that the 3M lens is somewhat expensive to manufacture in order to provide the required series of miniature ridges in the proper places on the very small lens implants. Therefore, it is desired to provide a dual-focus lens for implantation in the human eye which avoids the degradation produced by diffraction optics and can be easily and inexpensively manufactured.